The present invention relates to a database management system (DBMS) and more particularly, to a method for relocating data considering DBMS information.
Nowadays, there exist many applications constructed based on database (DB), and a database management system (DBMS), which is the software that manages the creation and maintenance of DB and offers functions to access data in DB easily is highly important. In particular, since the processing performance of the DBMS also determines the performance of an application used for the DB, an improvement in the processing performance of the DBMS is very vital.
One of features of the DB is to handle a great amount of data. To this end, in most of DBMS execution environments, a storage system having a large capacity or a plurality of storage systems are connected to a computer where the DBMS is executed to store data of the DB on the storage system. For this reason, when DB processing is carried out, an access to the storage system takes place and the performance of the DBMS is determined largely by the data access performance of the storage system. In a DBMS operating system, therefore, it is highly important to optimize the performance of the storage system and in particular, to optimize the location of data to be managed by the DBMS to physical storage devices.
A literature “Desining and Tuning for Performance Release 2 (8.1.6)”, A76992-01, Oracle Corp., Chapter 20 (which will be referred to as Document 1) describes I/O tuning in the Oracle8i as a relational DBMS (RDBMS). Described in Document 1 as explanations related to the tuning of internal operation of the RDBMS and the tuning of data location are that a log file is stored in physical storage device separated from another data file, that load balancing works effectively by storing data among disks with striping, that table data and index data related thereto become effective when stored in different physical storage devices, and that data not related to the RDBMS is stored in a different physical storage device.
U.S. Pat. No. 6,035,306 (referred to as Document 2) discloses a technique relating to a performance analysis tool considering mapping between DBMS, file system, volume manager and storage system. The performance analysis tool displays workloads of objects in each layers on a screen. At this time, the tool, considering the above mapping, provides a function of easily displaying a view workloads of objects in other layers associated with the first-mentioned objects. Among ones of the objects of the volume manager layers which are stored in a group of high-load storage devices, the tool also has a function of creating an object relocating plan to migrate a second-high load object to a group of lower-load storage devices.
JP-A-9-274544 (Document 3) discloses a technique for improving the access performance of a storage system wherein logical storage devices to be used by a computer are located to physical storage devices for actual storage of data, by dynamically changing the location of the logical storage devices to the physical storage devices. When part of the data stored in physical storage device having a high workload is migrated to another physical storage device based on the above dynamical data migration function, it prevents a particular physical storage device from having a high workload, thus enhancing the performance when viewed from the entire storage system. Also disclosed in Document 3 is a method for automatically executing operations based on the dynamic location change function for a higher performance.
JP-A-2001-67187 (Document 4) discloses, in a storage system wherein logical storage devices to be accessed by a computer are located to physical storage devices for actual storage of data and which has a function of dynamically changing the location of the logical storage devices to the physical storage devices, a technique which divides the physical storage devices into groups having different attributes, creates a plan of changing the location of the physical storage devices to the physical storage devices considering the group division and automatically changes the location of the logical storage devices according to the location change plan. At the time of creating the location change plan, the physical storage devices are grouped according to the attributes, the location change plan is created to select one of the physical storage devices belonging to the group of the physical storage devices having a suitable characteristics as a location destination of one of the logical storage devices, thereby creating a good location change plan.
Described in Document 1 are items to be considered by an administrator when determining the location of data. At present, there exist storage apparatuses which have many physical storage devices internally and are shared by many computers. In such storage apparatuses, in many cases, the logical storage devices to be recognized by a computer are assigned to the area in the physical storage devices for actual data storage. In the case of using such storage apparatuses, it is difficult for humankind e.g., an administrator to grasp the full situations, and becomes even more difficult to grasp even problems explained in Document 1, if a computer system including such storage apparatuses does not have any support function. Even when he/she can grasp the problems, if the computer system does not have a data migration function, back up and restore operations are required to relocate data on the storage devices which requires a large amount of labor.
The technique described in Document 2 can realize a function of creating a data relocation plan based on the workloads of objects in volume manager layers. When it is desired to obtain a higher access performance from the storage devices, it is required to determine the data location in the storage devices taking features in the DBMS layers into consideration. However, the solution to this aspect is not mentioned in Document 2.
In the techniques described in Documents 3 and 4, since consideration is paid only to the workloads and sequential access performance as features of data, good location cannot be always attained when viewed from the application. For example, in a DBMS, it is often to access table data and index data associated therewith at the same time. Such data might be located to an identical physical storage device. In this case, an access contention takes place, thus undesirably degrading the access performance of the storage system.